Space-charge effects in a CRT with post-deflection acceleration

The theory which gives the space-charge contribution to the trace width in a cathode ray tube (CRT) is extended to mesh-expansion postdeflection acceleration (PDA) tubes. This is done in an approximation that neglects the space-charge repulsion in the final beam acceleration region of the CRT. Comparison with experimental results indicates that the approximation is valid. The problem leads to nonelementary functions that must be solved numerically. A graph giving the space-charge contribution to trace width is provided for a range of basic tube parameters. The results are also interesting for qualitative understanding of the role that space charge plays in PDA tubes.